package com.yhq.yhqproject.base.common.utils;

import java.net.InetAddress;
import java.net.UnknownHostException;

public class IdGen {

    private long workerId;
    private long datacenterId;
    private long sequence = 0L;
    private long workerIdBits = 5L;
    private long datacenterIdBits = 5L;
    /**
     * 最大支持机器节点数0~31，一共32个
     */
    private long maxWorkerId = -1L ^ (-1L << workerIdBits);
    private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    private long sequenceBits = 12L;
    private long workerIdShift = sequenceBits;
    private long datacenterIdShift = sequenceBits + workerIdBits;
    private long timestampLeftShift = datacenterIdShift + datacenterIdBits;
    private long sequenceMask = -1L ^ (-1L << sequenceBits);
    private long lastTimestamp = -1L;

    private static class IdGenHolder {
        private static final IdGen instance = new IdGen();
    }

    public static IdGen get() {
        return IdGenHolder.instance;
    }

    public void init() {
        String ip;
        try {
            ip = InetAddress.getLocalHost().getHostAddress();
            int hash = toHash(ip);
            this.workerId = Math.abs(hash % 32);
            this.datacenterId = (int) (Math.random() * 32);
        } catch (UnknownHostException e) {
            e.printStackTrace();
        }

    }

    public IdGen() {
        init();
    }

    public IdGen(long workerId, long datacenterId) {
        if (workerId > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
        }
        if (datacenterId > maxDatacenterId || datacenterId < 0) {
            throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
        }
        this.workerId = workerId;
        this.datacenterId = datacenterId;
    }

    public synchronized String nextSid() {
        return nextId() + "";
    }


    public synchronized long nextId() {
        //获取当前毫秒数
        long timestamp = timeGen();
        // 如果服务器时间有问题(时钟后退) 报错。
        if (timestamp < lastTimestamp) {
            throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }
        // 如果上次生成时间和当前时间相同,在同一毫秒内
        if (lastTimestamp == timestamp) {
            // sequence自增，因为sequence只有12bit，所以和sequenceMask相与一下，去掉高位
            sequence = (sequence + 1) & sequenceMask;
            // 判断是否溢出,也就是每毫秒内超过4095，当为4096时，与sequenceMask相与，sequence就等于0
            if (sequence == 0) {
                // 自旋等待到下一毫秒
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            // 如果和上次生成时间不同,重置sequence，就是下一毫秒开始，sequence计数重新从0开始累加
            sequence = 0L;
        }
        lastTimestamp = timestamp;
        // 最后按照规则拼出ID。
        // 000000000000000000000000000000000000000000 00000 00000 000000000000

        // time datacenterId workerId sequence
        long twepoch = 1288834974657L;
        return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;
    }

    public static int toHash(String key) {
        int arraySize = 11113; // 数组大小一般取质数
        int hashCode = 0;
        for (int i = 0; i < key.length(); i++) { // 从字符串的左边开始计算
            int letterValue = key.charAt(i) - 96;// 将获取到的字符串转换成数字，比如a的码值是97，则97-96=1
            // 就代表a的值，同理b=2；
            hashCode = ((hashCode << 5) + letterValue) % arraySize;// 防止编码溢出，对每步结果都进行取模运算
        }
        return hashCode;
    }

    protected long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }

    protected long timeGen() {
        return System.currentTimeMillis();
    }

}
